From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752140AbcFFT66 (ORCPT ); Mon, 6 Jun 2016 15:58:58 -0400 Received: from smtp-outbound-2.vmware.com ([208.91.2.13]:50274 "EHLO smtp-outbound-2.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750831AbcFFT65 (ORCPT ); Mon, 6 Jun 2016 15:58:57 -0400 From: Nadav Amit To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: nadav.amit@gmail.com, Nadav Amit , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Morton , Dave Hansen , Rik van Riel , Mel Gorman , Andy Lutomirski , "Kirill A. Shutemov" , Michal Hocko , Vladimir Davydov , Jerome Marchand , Johannes Weiner , Hugh Dickins , Minchan Kim , linux-mm@kvack.org (open list:MEMORY MANAGEMENT) Subject: [PATCH] x86/mm: Change barriers before TLB flushes to smp_mb__after_atomic Date: Fri, 27 May 2016 20:16:51 -0700 Message-Id: <1464405413-7209-1-git-send-email-namit@vmware.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When (current->active_mm != mm), flush_tlb_page() does not perform a memory barrier. In practice, this memory barrier is not needed since in the existing call-sites the PTE is modified using atomic-operations. This patch therefore modifies the existing smp_mb in flush_tlb_page to smp_mb__after_atomic and adds the missing one, while documenting the new assumption of flush_tlb_page. In addition smp_mb__after_atomic is also added to set_tlb_ubc_flush_pending, since it makes a similar implicit assumption and omits the memory barrier. Signed-off-by: Nadav Amit --- arch/x86/mm/tlb.c | 9 ++++++++- mm/rmap.c | 3 +++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index fe9b9f7..2534333 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -242,6 +242,10 @@ out: preempt_enable(); } +/* + * Calls to flush_tlb_page must be preceded by atomic PTE change or + * explicit memory-barrier. + */ void flush_tlb_page(struct vm_area_struct *vma, unsigned long start) { struct mm_struct *mm = vma->vm_mm; @@ -259,8 +263,11 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long start) leave_mm(smp_processor_id()); /* Synchronize with switch_mm. */ - smp_mb(); + smp_mb__after_atomic(); } + } else { + /* Synchronize with switch_mm. */ + smp_mb__after_atomic(); } if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids) diff --git a/mm/rmap.c b/mm/rmap.c index 307b555..60ab0fe 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -613,6 +613,9 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, { struct tlbflush_unmap_batch *tlb_ubc = ¤t->tlb_ubc; + /* Synchronize with switch_mm. */ + smp_mb__after_atomic(); + cpumask_or(&tlb_ubc->cpumask, &tlb_ubc->cpumask, mm_cpumask(mm)); tlb_ubc->flush_required = true; -- 2.7.4